The present disclosure relates generally to light emitting diode (LED) assemblies, and more specifically, to LED assembly that has an omnidirectional light field.
LED has been used in different kinds of appliances in our daily life, such as traffic lights, car headlights, street lamps, computer indicators, flashlights, LCD backlight modules, and so on. Beside the semiconductor manufacturing process in the front end, the LED chips used in these appliances should go through LED packaging in the back end.
LED packaging mainly provides mechanical, electrical, thermal, and optical supports to LED chips. LED chips, which are a kind of semiconductor products, are prone to performance degradation, or aging, if exposed for a long time in an atmosphere full of humidity or chemical. Epoxy resin is commonly used in LED packaging to cover or seal LED chips, such that LED chips are effectively isolated from detrimental atmosphere. Furthermore, LED packaging should take heat dissipation and luminance extraction into consideration, in order to make LED assembly more power-saving and reliable. Heat generated in an LED chip must be dissipated efficiently. Otherwise, heat accumulated in the PN junction of an LED chip will damage or degrade its performance, shortening its lifespan. Optical design is also a key factor when designing of LED packaging. Light emitted from an LED chip must be transmitted in a way that results in certain luminance distribution with certain intensity.
The design for packaging a white LED further needs to consider color temperature, color rendering index, phosphor, etc. The white LED could be provided by phosphor converting a portion of blue light from a blue LED chip into green/yellow light such that the mixture of the lights is perceived as white light by human eyes. Because human eyes are vulnerable to high-intensity blue light, the blue light from a blue LED chip in a white LED package should not go outside directly without its intensity being attenuated. In other words, the blue light should be kind of “sealed” or “capsulated” so as to prevent blue light leakage to human eyes.
In order to make products more competitive in the market, LED package manufactures constantly pursue packaging processes which are reliable, low-cost, and high-yield.